Tree frog survives in city as others croak it

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If you stroll through Melbourne's parks and gardens at night you may notice the high-pitched trilling of a frog.

What you may not be aware of is that the southern brown tree frog, and its distinctive call, resembling a "brr, brr, brr, brrrr" is alone in the inner urban environment. Eight to 10 varieties once lived in the city; now this tree frog is the only species found. It makes up about half of all frogs in the suburbs.

A study recently completed by Deakin University's Kirsten Parris has been unlocking the mystery of how this tough amphibian is beating the odds.

Dr Parris said the secret of this super frog is that being a tree frog means it can scale the bluestone borders of the ponds and water features in Melbourne's parks and use the aquatic environments to breed.

While other varieties of frogs could sometimes get into the ponds to lay their eggs, the resulting baby frogs drowned when they developed lungs and lost their tadpole's gills, she said.

"They have large sticky toes so they can get in and out of the ponds," she said. "A wall that is 30 centimetres high is pretty daunting to a small frog."

Frogs are an important part of the ecosystem, and provide food for tortoises and fish as tadpoles, and for birds and snakes when fully grown.

Dr Parris said that if the decline of urban frogs was to be reversed, some of the pond walls would have to be removed and more shrubs planted to give the amphibians a chance to hide from predators.

Busy roads that disrupt natural movements are also a problem.

Some frog species that have disappeared from our parks and gardens may have to be relocated from other areas to repopulate the areas in which they once lived, Dr Parris said.